The instant invention relates to improving the uniformity of a pneumatic tire by measuring and correcting excessive variation in the free radical run-out of the tire during such rotation of the tire.
Various constructions of pneumatic vehicle tires are well known. Ideally, these well-known constructions will yield tires which are quite uniform. It is recognized, however, that during the manufacturing process some deviations from the ideal occur. Experience has shown that minor deviations can be tolerated and do not contribute, to any significant degree, to an objectionable level of non-uniformity such as would adversely affect the ride quality of the tire. However, when deviations exceed certain levels, they will have an adverse affect on the ride and handling characteristics of the vehicle on which they are mounted.
One source of tire non-uniformity is the variation in the forces which are exerted radially between the tire and the road surface as the tire rolls along such surface under a normal load. These variations are usually described as radial force variations. Another source of non-uniformity is the eccentricity of the tire, that is, its deviation from a perfect circle. This eccentricity is also known as free radical run-out. Measurements to determine the deviation in the eccentricity of the tire are taken at the surface of the tread, usually at the shoulders and center. If these measurements exhibit excessive variations, they can be corrected to an acceptable level by a process of grinding the tread in the areas of maximum radial deviation. This method of correcting non-uniformity is quite satisfactory but does not remove all tire anomalies that contribute to or cause unsatisfactory rides and failing conditions.
The tire industry has adopted a sophisticated and expensive method of correcting tire non-uniformities that are attributable to the variations in radial force and has ignored, generally, the radial run-out quality of the tire. The devices for measuring and correcting radial force variations in a tire are well known in the tire art and are usually indentified as tire uniformity graders (TUG) or tire uniformity optimizers (TUO). Such devices usually include a wheel and axle assembly on which the tire to be evaluated is mounted and a test-wheel in contact with the tire. The tire is forcibly held against the test-wheel, the applied force thereby providing a predetermined load on the tire, and when the test-wheel is rotated, the tire rotates with it. As the tire rotates, the variation in the radial force on the axle on which the tire is mounted is measured. Correction for excessive variation in radial forces usually involves grinding tire tread around its circumference along one or both shoulders at selected areas.
In most cases where tire manufacturers have adopted radial force variation correction machines, correction for radial run-out has been abandoned because of the added expense of an additional processing step and the probability of correcting one area of tire-non-uniformity at the expense of another by grinding the tire tread by two independent and separate means. In other words, regardless of which of the two correction methods were to be used first, both correction methods grind the tire in selected areas. It is probable that after a tire is corrected for radial force variation, the subsequent radial run-out correction may create new objectionable radial forces. If the radial run-out were corrected first, the subsequent radial force correction may cancel the benefit of the radial run-out correction. Unfortunately, the radial force variations and the radial run-out variations of a tire do not occur, necessarily, in the same place on the tire. In other words, correcting for one will not necessarily correct for the other.
Automobile manufacturers are now demanding that tires supplied to them meet certain uniformity criteria. Accordingly, they require data certifying that the tires supplied to them meet their prescribed limits for radial run-out variation as well as radial force variation. Therefore, the instant invention is designed for operation on existing tire uniformity machines (for radial force variation measurement and correction) to provide measurement and correction for variation in free radial run-out. Existing tire uniformity machines are equipped with shoulder grinders for radial force variation correction. This invention modifies existing uniformity machines by providing a concentricity grinder at the tread center and a three point probe for free radial run-out detection. Existing tread shoulder grinders of TUG machines are modified with sensors and a concentricity measuring system.